Halfmoon · ADU cost
What it costs to build an ADU in Halfmoon, NY
An 800 sq ft accessory dwelling unit in Halfmoon runs roughly $200k–260k, or about $249–327/sq ft, and that per-square-foot figure sits deliberately above the $204–268/sq ft a full house costs here. An ADU still needs one whole kitchen, one whole bath, its own service panel and its own heating plant no matter how small you draw it, and those costs do not shrink with the floor plan, so they land on half the square footage and push the rate up. Whether the town will let you build one is a separate question from what it costs, and it gets answered parcel by parcel rather than townwide, since the Town of Halfmoon maps 12 districts that treat accessory units differently from one another, so read the table below as a starting point rather than a verdict.
ADU cost by size in Halfmoon
Standard finish, slab on grade, on a flat and clear part of the lot, general-contractor margin included. These are structure costs at Saratoga County pricing, before the service and septic work a second dwelling can trigger.
| Size | Type | $ / sq ft | Estimated total |
|---|---|---|---|
| 400 sq ft | Studio | $331–$433 | $130k–175k |
| 600 sq ft | One bedroom | $276–$362 | $165k–215k |
| 800 sq ft | One bedroom, larger | $249–$327 | $200k–260k |
| 1,000 sq ft | Two bedroom | $233–$305 | $235k–305k |
400 sq ft — One room plus a bath. Garage conversions and small backyard cottages land here.
600 sq ft — The most common detached build - a real bedroom, full kitchen, one bath.
800 sq ft — Room for a proper living area. Still a single bath and one kitchen.
1,000 sq ft — About as large as most codes allow an accessory unit to go.
Why the rate is higher than a house
The systems below are priced for an 800 sq ft unit. The middle column is what each system would cost if it simply shrank with the floor plan; the left column is what it actually costs once you account for the equipment a dwelling needs one of regardless of size. The gap between the two columns is the whole reason small builds price the way they do.
| System | $ / sq ft in an ADU | If it scaled with floor area | Fixed per unit |
|---|---|---|---|
| Site work | $7–$11 | $7 | — |
| Foundation | $16–$23 | $16 | — |
| Framing | $25–$32 | $25 | — |
| Envelope - roof, siding, windows | $32–$41 | $32 | — |
| Plumbing | $28–$34 | $16 | 55% |
| Electrical | $18–$24 | $13 | 35% |
| HVAC | $23–$28 | $15 | 45% |
| Insulation | $7–$9 | $7 | — |
| Interior finishes | $32–$43 | $27 | 15% |
| Millwork & cabinetry | $18–$28 | $11 | 55% |
The fixed-per-unit share is a modeling assumption, not a figure from the code: it is our estimate of how much of each system's budget buys equipment a dwelling needs exactly one of - a kitchen rough-in, a bath group, a service panel, a heating plant - and therefore does not shrink when the unit does. Site work, foundation, framing, envelope and insulation are treated as scaling straight with floor area, which understates the premium slightly, because a small building carries more envelope per square foot of floor than a large one.
What the Halfmoon code says about accessory units
Whether you can build one, and how large, is decided by the district your parcel sits in rather than by the town as a whole. The table shows how each mapped district treats ADUs alongside the lot and setback standards a second unit still has to fit inside. District boundaries and conditions vary, so treat it as a starting point and confirm the district that applies to your parcel.
| District | Min lot | Setbacks F / S / R | Max height | ADU |
|---|---|---|---|---|
| Agriculture-Residence (single-family dwelling: min lot 20,000 sf with public sewer AND water, 30,000 sf with sewer OR water, 40,000 sf with no utilities; min lot width 100 ft on full utilities, 150 ft otherwise; 20% maximum building coverage; 35 ft height; 50 ft front, 15 ft one side / 30 ft both sides, 50 ft rear. A FARM is held to a larger standard: 80,000 sf, 150 ft width, 30% coverage, and 50 ft one side / 100 ft both sides. A two-family dwelling is a special-permit use at 40,000 sf regardless of utility service. Permitted uses include farms, equestrian facilities, commercial woodlots and reforestation areas alongside one-family dwellings. Corridor exception: Schedule A's 'Exceptions to minimum dimensions listed in all districts' block overrides the district minimums along named roads regardless of zoning — Route 9 25,000 sf / 150 ft; Route 146 28,000 sf / 150 ft with a 70 ft front yard; Route 9 at Grooms Road 25,000 sf / 150 ft; Route 9 at Guideboard Road 25,000 sf / 150 ft; Route 236 25,000 sf / 150 ft; Routes 4 and 32 west side only a 70 ft front yard, both sides 25,000 sf / 150 ft. Check the frontage road before trusting the district figure.) | 0.46 ac | 50 / 15 / 50 ft | 35 ft | No |
| Residence 1 (min lot 20,000 sf with public sewer AND water, 30,000 sf with sewer OR water, 40,000 sf with no utilities; min lot width 100 ft on full utilities, 150 ft otherwise; 20% maximum building coverage; 35 ft height; 50 ft front, 15 ft one side / 30 ft both sides, 50 ft rear. Schedule A gives A-R and R-1 a SHARED row — their single-family standards are genuinely identical; the districts differ in what else they permit, not in dimensions. A two-family dwelling is a special-permit use at 40,000 sf regardless of utility service, and its coverage rises to 30% where there are no utilities. Corridor exception: Schedule A's 'Exceptions to minimum dimensions listed in all districts' block overrides the district minimums along named roads regardless of zoning — Route 9 25,000 sf / 150 ft; Route 146 28,000 sf / 150 ft with a 70 ft front yard; Route 9 at Grooms Road 25,000 sf / 150 ft; Route 9 at Guideboard Road 25,000 sf / 150 ft; Route 236 25,000 sf / 150 ft; Routes 4 and 32 west side only a 70 ft front yard, both sides 25,000 sf / 150 ft. Check the frontage road before trusting the district figure.) | 0.46 ac | 50 / 15 / 50 ft | 35 ft | No |
| Residence 2 (Schedule A states 'General — Same as R-1 above', so the dimensional standards are identical to R-1: min lot 20,000 sf with public sewer AND water, 30,000 sf with sewer OR water, 40,000 sf with no utilities; 100 ft lot width on full utilities, 150 ft otherwise; 20% maximum building coverage; 35 ft height; 50 ft front, 15 ft one side / 30 ft both sides, 50 ft rear. R-2 is a distinct mapped district, not an overlay — what sets it apart is that a MOBILE HOME PARK is a special-permit use here, regulated by the Town's Trailer Ordinance rather than by Schedule A. Corridor exception: Schedule A's 'Exceptions to minimum dimensions listed in all districts' block overrides the district minimums along named roads regardless of zoning — Route 9 25,000 sf / 150 ft; Route 146 28,000 sf / 150 ft with a 70 ft front yard; Route 9 at Grooms Road 25,000 sf / 150 ft; Route 9 at Guideboard Road 25,000 sf / 150 ft; Route 236 25,000 sf / 150 ft; Routes 4 and 32 west side only a 70 ft front yard, both sides 25,000 sf / 150 ft. Check the frontage road before trusting the district figure.) | 0.46 ac | 50 / 15 / 50 ft | 35 ft | No |
| Residence 3 — the Town's multifamily residence district (single-family and two-family dwellings follow the R-1 standards: 20,000 sf on full utilities, 20% coverage, 50 ft rear. The district's own standards apply to larger buildings — a THREE-FAMILY dwelling needs 30,000 sf with public sewer and water, 40,000 sf with one, 50,000 sf with none; a FOUR-FAMILY dwelling needs 40,000 / 50,000 / 60,000 sf on the same ladder. For both, lot width is 150 ft, maximum building coverage 25%, height 35 ft, and yards are 50 ft front, 15 ft one side / 30 ft both sides, 30 ft rear — note the rear yard drops from R-1's 50 ft to 30 ft. The recorded figures are the single/two-family case, which is the entry point; step up to the 3- and 4-family figures above for multifamily. Corridor exception: Schedule A's 'Exceptions to minimum dimensions listed in all districts' block overrides the district minimums along named roads regardless of zoning — Route 9 25,000 sf / 150 ft; Route 146 28,000 sf / 150 ft with a 70 ft front yard; Route 9 at Grooms Road 25,000 sf / 150 ft; Route 9 at Guideboard Road 25,000 sf / 150 ft; Route 236 25,000 sf / 150 ft; Routes 4 and 32 west side only a 70 ft front yard, both sides 25,000 sf / 150 ft. Check the frontage road before trusting the district figure.) | 0.46 ac | 50 / 15 / 50 ft | 35 ft | No |
| Professional Office/Residence (min lot 25,000 sf with public sewer AND water, 35,000 sf with sewer OR water, 45,000 sf with no utilities; 150 ft lot width; 20% maximum building coverage; 35 ft height; 70 ft front — the deepest front yard in the Town alongside the Route 146 corridor; 10 ft one side / 25 ft both sides, 30 ft rear; minimum 20% GREEN SPACE, a separate landscaped-area requirement on top of the coverage cap. All uses allowed by special permit in R-1 are also available here. Corridor exception: Schedule A's 'Exceptions to minimum dimensions listed in all districts' block overrides the district minimums along named roads regardless of zoning — Route 9 25,000 sf / 150 ft; Route 146 28,000 sf / 150 ft with a 70 ft front yard; Route 9 at Grooms Road 25,000 sf / 150 ft; Route 9 at Guideboard Road 25,000 sf / 150 ft; Route 236 25,000 sf / 150 ft; Routes 4 and 32 west side only a 70 ft front yard, both sides 25,000 sf / 150 ft. Check the frontage road before trusting the district figure.) | 0.57 ac | 70 / 10 / 30 ft | 35 ft | No |
| Commercial (min lot 25,000 sf with public sewer AND water, 35,000 sf with sewer OR water, 45,000 sf with no utilities; 150 ft lot width; 50% maximum building coverage subject to site plan review and approval; 35 ft height, and heights above 35 ft may be submitted to the Planning Board as part of the site plan; 50 ft front, 15 ft one side / 30 ft both sides, 25 ft rear; minimum 20% green space. Where a side or rear yard adjoins a residential zone the transition yard requirements of § 165-32F apply instead. The 25,000 sf minimum is itself conditioned on site plan approval and on the ability to meet parking, setback and green-space requirements and to connect to public sewer and water. Corridor exception: Schedule A's 'Exceptions to minimum dimensions listed in all districts' block overrides the district minimums along named roads regardless of zoning — Route 9 25,000 sf / 150 ft; Route 146 28,000 sf / 150 ft with a 70 ft front yard; Route 9 at Grooms Road 25,000 sf / 150 ft; Route 9 at Guideboard Road 25,000 sf / 150 ft; Route 236 25,000 sf / 150 ft; Routes 4 and 32 west side only a 70 ft front yard, both sides 25,000 sf / 150 ft. Check the frontage road before trusting the district figure.) | 0.57 ac | 50 / 15 / 25 ft | 35 ft | No |
| Light Industrial-Commercial (min lot 40,000 sf with public sewer AND water, 50,000 sf with sewer OR water, 60,000 sf with no utilities; 150 ft lot width; 50% maximum building coverage subject to site plan review; 35 ft height, with greater heights available through site plan review; 50 ft front, 15 ft one side / 30 ft both sides, 30 ft rear; minimum 20% green space. Transition yard requirements under § 165-32F apply where the lot adjoins a residential zone. Corridor exception: Schedule A's 'Exceptions to minimum dimensions listed in all districts' block overrides the district minimums along named roads regardless of zoning — Route 9 25,000 sf / 150 ft; Route 146 28,000 sf / 150 ft with a 70 ft front yard; Route 9 at Grooms Road 25,000 sf / 150 ft; Route 9 at Guideboard Road 25,000 sf / 150 ft; Route 236 25,000 sf / 150 ft; Routes 4 and 32 west side only a 70 ft front yard, both sides 25,000 sf / 150 ft. Check the frontage road before trusting the district figure.) | 0.92 ac | 50 / 15 / 30 ft | 35 ft | No |
| Industrial (min lot 40,000 sf with public sewer AND water, 50,000 sf with sewer OR water, 60,000 sf with no utilities; 150 ft lot width; 50% maximum building coverage subject to site plan review; 35 ft height, with greater heights available through site plan review; 50 ft front, 15 ft one side / 30 ft both sides, 25 ft rear; minimum 20% green space. Transition yard requirements under § 165-32F apply where the lot adjoins a residential zone. Corridor exception: Schedule A's 'Exceptions to minimum dimensions listed in all districts' block overrides the district minimums along named roads regardless of zoning — Route 9 25,000 sf / 150 ft; Route 146 28,000 sf / 150 ft with a 70 ft front yard; Route 9 at Grooms Road 25,000 sf / 150 ft; Route 9 at Guideboard Road 25,000 sf / 150 ft; Route 236 25,000 sf / 150 ft; Routes 4 and 32 west side only a 70 ft front yard, both sides 25,000 sf / 150 ft. Check the frontage road before trusting the district figure.) | 0.92 ac | 50 / 15 / 25 ft | 35 ft | No |
| Clean Manufacturing (shares the M-1 row in Schedule A: min lot 40,000 sf with public sewer AND water, 50,000 sf with sewer OR water, 60,000 sf with no utilities; 150 ft lot width; 50% maximum building coverage subject to site plan review; 35 ft height, with greater heights available through site plan review; 50 ft front, 15 ft one side / 30 ft both sides, 25 ft rear; minimum 20% green space. IMPORTANT: any RESIDENTIAL use in M-2 must instead meet the Schedule A requirements for residential uses in the R-1/A-R districts, per Schedule A note 8. Corridor exception: Schedule A's 'Exceptions to minimum dimensions listed in all districts' block overrides the district minimums along named roads regardless of zoning — Route 9 25,000 sf / 150 ft; Route 146 28,000 sf / 150 ft with a 70 ft front yard; Route 9 at Grooms Road 25,000 sf / 150 ft; Route 9 at Guideboard Road 25,000 sf / 150 ft; Route 236 25,000 sf / 150 ft; Routes 4 and 32 west side only a 70 ft front yard, both sides 25,000 sf / 150 ft. Check the frontage road before trusting the district figure.) | 0.92 ac | 50 / 15 / 25 ft | 35 ft | No |
| Neighborhood Business (min lot 20,000 sf; 100 ft lot width; 20% maximum building coverage; 35 ft height; 50 ft front, 10 ft one side / 25 ft both sides, 30 ft rear; minimum 20% green space. The Planning Board may consider a minimum 10,000 sf lot under the conditions in § 165-17B(3), so this is the one district with an explicit route to a half-size lot. The smallest-lot commercial district in the Town. Corridor exception: Schedule A's 'Exceptions to minimum dimensions listed in all districts' block overrides the district minimums along named roads regardless of zoning — Route 9 25,000 sf / 150 ft; Route 146 28,000 sf / 150 ft with a 70 ft front yard; Route 9 at Grooms Road 25,000 sf / 150 ft; Route 9 at Guideboard Road 25,000 sf / 150 ft; Route 236 25,000 sf / 150 ft; Routes 4 and 32 west side only a 70 ft front yard, both sides 25,000 sf / 150 ft. Check the frontage road before trusting the district figure.) | 0.46 ac | 50 / 10 / 30 ft | 35 ft | No |
| Waterfront Mixed Use (shares the C-1 row in Schedule A: min lot 25,000 sf with public sewer AND water, 35,000 sf with sewer OR water, 45,000 sf with no utilities; 150 ft lot width; 50% maximum building coverage subject to site plan review; 35 ft height, with greater heights available through site plan review; 50 ft front, 15 ft one side / 30 ft both sides, 25 ft rear; minimum 20% green space. IMPORTANT: any RESIDENTIAL use in W-1 must instead meet the Schedule A requirements for residential uses in the R-1/A-R districts, per Schedule A note 8 — so a dwelling here is held to the 20,000 sf residential standard, not the 25,000 sf commercial one. Corridor exception: Schedule A's 'Exceptions to minimum dimensions listed in all districts' block overrides the district minimums along named roads regardless of zoning — Route 9 25,000 sf / 150 ft; Route 146 28,000 sf / 150 ft with a 70 ft front yard; Route 9 at Grooms Road 25,000 sf / 150 ft; Route 9 at Guideboard Road 25,000 sf / 150 ft; Route 236 25,000 sf / 150 ft; Routes 4 and 32 west side only a 70 ft front yard, both sides 25,000 sf / 150 ft. Check the frontage road before trusting the district figure.) | 0.57 ac | 50 / 15 / 25 ft | 35 ft | No |
| Waterfront Commercial (W-2 appears TWICE in Schedule A and the applicable row depends on the use: for uses also permitted in the W-1 District it follows the C-1 row — 25,000 sf with public sewer AND water, 35,000 sf with one, 45,000 sf with none; for uses also permitted in the M-2 District it follows the M-1 row — 40,000 / 50,000 / 60,000 sf on the same utility ladder. Both rows otherwise agree: 150 ft lot width, 50% maximum building coverage subject to site plan review, 35 ft height with greater heights available through site plan review, 50 ft front, 15 ft one side / 30 ft both sides, 25 ft rear, minimum 20% green space. The recorded minimum is the smaller W-1-type figure; step up to 40,000 sf for manufacturing-type uses. RESIDENTIAL uses in W-2 must meet the R-1/A-R residential requirements per Schedule A note 8. Corridor exception: Schedule A's 'Exceptions to minimum dimensions listed in all districts' block overrides the district minimums along named roads regardless of zoning — Route 9 25,000 sf / 150 ft; Route 146 28,000 sf / 150 ft with a 70 ft front yard; Route 9 at Grooms Road 25,000 sf / 150 ft; Route 9 at Guideboard Road 25,000 sf / 150 ft; Route 236 25,000 sf / 150 ft; Routes 4 and 32 west side only a 70 ft front yard, both sides 25,000 sf / 150 ft. Check the frontage road before trusting the district figure.) | 0.57 ac | 50 / 15 / 25 ft | 35 ft | No |
Costs an ADU adds that a house does not
- Septic and water A second dwelling adds bedrooms to the design flow, which on an unsewered parcel often means expanding or replacing the existing system rather than tapping it. This is the single most common reason an ADU budget moves after design, and it is site-specific enough that no model should quote it - get it evaluated early.
- Utility service National Grid territory. A detached unit needs power run to it, and whether it goes on its own meter or subfeeds the main house changes both the cost and the permit path.
- Access and parking Many codes require an added parking space for the accessory unit, and a detached unit usually needs a driveway extension or a path, both of which count against a lot-coverage or impervious-surface cap.
- Short-term rentalsNo local short-term-rental law on record - which is not the same as permission. Short-term rental status not confirmed for the Town of Halfmoon. Chapter 165 (Zoning) defines no short-term-rental, transient-occupancy or tourist-home use, Schedule A lists none, and a review of all 46 chapters of the Town Code found no rental or short-term-rental chapter. The nearest defined use is the BED-AND-BREAKFAST HOMESTAY — a private OWNER-OCCUPIED dwelling with no more than three guest rooms, subordinate to the main residential use, breakfast served to overnight guests only — which is not a whole-house short-term rental. Absence of a found STR provision is NOT permission — call Building & Code Enforcement at (518) 371-7410 x2260 before listing a property. Separately, since 2025 New York State requires every short-term-rental host to register the unit with the State through the county registry, regardless of what the municipality allows. Separate question from whether you can build the unit.
- Building dept(518) 371-7410 x2260
Sizing up a specific parcel in Halfmoon?
Aldo pulls the exact zoning district, setbacks, and build feasibility for any parcel — before you buy. Enter your email to open Aldo and run your free report.
Building a full house instead?
A standard-finish house in Halfmoon runs $204–268/sq ft, about $370k–480k at 1,800 sq ft , plus roughly $28,700 for a conforming lot. See what it costs to build a house in Halfmoon.
ADU cost in nearby towns
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More on Halfmoon: Can you build an ADU here? · Zoning for new construction · Saratoga County build cost
ADU cost in Halfmoon: common questions
How much does it cost to build an ADU in Halfmoon, NY?
An 800 sq ft accessory dwelling unit in Town of Halfmoon runs roughly $200k–260k at a standard finish, general-contractor margin included. A 400 sq ft studio runs about $130k–175k. Those are structure costs on an easy site and do not include the septic, water or electrical service work a second unit often triggers.
Why does an ADU cost more per square foot than a house in Halfmoon?
Because a lot of a dwelling's cost is per dwelling, not per square foot. One kitchen, one bath group, one service panel and one heating plant cost about the same in an 800 sq ft cottage as in a 1,800 sq ft house, so on the smaller unit they get spread over less than half the floor area. That is why an ADU here prices at $249–327/sq ft against $204–268/sq ft for a full house, even though it is the same trades doing the same work.
Are ADUs allowed in Halfmoon?
Town of Halfmoon has 12 districts. All districts prohibit ADUs. Check the specific address with the free ADU checker or confirm with the building department at (518) 371-7410 x2260 before you spend money on design.
Can I rent an ADU in Halfmoon short term?
No local short-term-rental law on record - which is not the same as permission for Town of Halfmoon. ADU rules and short-term-rental rules are set separately, so a unit you are allowed to build is not automatically one you are allowed to rent nightly. Confirm both before you underwrite the build on short-term-rental income.
ADU costs are modeled estimates in current 2026 dollars at the Saratoga County regional index, general-contractor margin included, derived from Offsite's cost engine with a stated adjustment for the equipment a dwelling needs one of regardless of size. They are planning numbers for decision-support only - not a bid, quote, or guarantee, and not legal, architectural or engineering advice. They cover the structure and exclude septic expansion, utility service runs, site work beyond a flat and clear pad, and permit fees. ADU eligibility, size, owner-occupancy and permit conditions in the Town of Halfmoon vary by district and often carry exceptions this page does not show; zoning last reviewed 2026-07-27; verify with the building department at (518) 371-7410 x2260 before relying on any answer. Sources: Offsite / Aldo cost engine (costEngine.js + constants.js); zoning dataset (municipalData.js).